Fuel injection system for an internal combustion engine

ABSTRACT

The invention relates to a fuel injection system for an internal combustion engine. The inventive fuel injection system comprises a high-pressure pump ( 1 ) for delivering the fuel from a fuel reservoir ( 2 ) and a number of fuel injectors ( 5 ) for injecting the fuel into the combustion chamber of the internal combustion engine. The system is further provided with a high-pressure fuel line ( 4 ) that links the high-pressure pump ( 1 ) with the fuel injectors ( 5 ) and that contains a high-pressure reservoir ( 3 ). A fuel return line ( 11 ) returns the fuel that was not injected by the fuel injectors ( 5 ) and a leakage line ( 12 ) returns the leakage amounts that occur at the fuel injectors ( 5 ). According to the invention the high-pressure fuel line ( 4 ), the fuel return line ( 11 ) and the leakage line ( 12 ) are combined in a common fuel line ( 13 ) which is characterized by cross-sections of flow that are separated from one another by walls and that correspond to the individual lines ( 4, 11, 12 ).

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a fuel injection system for an internalcombustion engine.

Fuel injection systems for internal combustion engines, particularlydiesel engines, are becoming increasingly wide-spread. The fuelinjection systems contain a high-pressure pump for delivering the fuelfrom a fuel reservoir, a number of fuel injectors for injecting the fuelinto the combustion space of the internal combustion engine, and ahigh-pressure fuel line. The high-pressure fuel line connects thehigh-pressure pump with the fuel injectors and contains a high-pressurereservoir for holding the fuel to be injected which is delivered by thehigh-pressure pump at a high pressure (common rail systems). Animportant advantage of such fuel injection systems is that, with respectto the injection start, the injection duration and the mass flow rate ofthe injected fuel per time unit, the injection operation can be veryprecisely adapted to the respective rotational speed condition and loadcondition of the internal combustion engine. In addition to thehigh-pressure fuel line which delivers the fuel from the high-pressurepump to the fuel injectors and holds the fuel at a high pressure, in thecase of these fuel injection systems, a fuel return flow line as well asa leakage line for returning the occurring leakage quantities, whichoccur at the fuel injectors or because of leakiness of the sealingpoints, are provided. The provision of these additional fuel lines isalready connected with high expenditures and, particularly in the caseof large-volume diesel engines, significant vibration-related problemsin connection to the mounting of the lines at the engine.

It is an object of the present invention to provide a fuel injectionsystem of the above-mentioned type which is improved with respect to theguidance of these fuel lines.

In accordance with one aspect of the invention, a fuel injection systemfor an internal combustion engine includes a high-pressure pump fordelivering the fuel from a fuel reservoir, a number of fuel injectorsfor injecting the fuel into the combustion space of the internalcombustion engine and a high-pressure fuel line. The high-pressure fuelline connects the high-pressure pump with the fuel injectors andcontains a high-pressure reservoir for holding the fuel to be injectedwhich is delivered at a high pressure by the high-pressure pump.Furthermore, a fuel return flow line for returning non-injected fuel anda leakage line are provided. According to the invention, thehigh-pressure fuel line, the fuel return flow line and the leakage lineare combined in a common fuel line with respective flow cross-sectionsfor each of the lines, which flow cross-sections are separated by walls.

A significant advantage of the fuel system according to the invention isthe fact that fastening parts, sealing and connecting elements requiredfor the separate mounting of the fuel return flow line and of theleakage line are eliminated. This avoids the risk of a functionalfailure of such elements, and no difficulties occur with respect tovibration problems of such lines.

In a preferred embodiment of the fuel injection system according to theinvention, the common fuel line is formed by three coaxially arranged,mutually surrounding line pipes. The interior pipe is the high-pressurefuel line, and it is surrounded by inner and outer jacket pipes whicheach enclose a flow cross-section and form the fuel return line and theleakage line. This results in the advantage that the high-pressure fuelline which, because of the required high-pressure stability, has a verymassive construction, forms a stable support for the surrounding jacketpipes, thereby neutralizing the vibration problems.

According to a preferred embodiment, the jacket pipes surrounding thehigh-pressure fuel line are provided with ducts on their interiorsurface, which ducts extend in the longitudinal direction and form theflow cross-sections of the fuel return line and of the leakage linerespectively.

In this case, the jacket pipes surrounding the high-pressure fuel linepreferably have webs on their inner surface between the ducts formingthe flow cross-sections of the fuel return line and the leakage linerespectively. The webs rest against the outer circumference of therespective inner line surrounded by the respective jacket pipe.

According to a preferred embodiment of the invention, the inner jacketpipe surrounding the high-pressure fuel line forms the leakage line, andthe outer jacket pipe surrounding the inner jacket pipe forms the fuelreturn line.

According to a preferred embodiment of the invention, the fuel injectorsof the injection system each have a common high-pressure connectionprovided with a high-pressure duct mouth for the connection of thehigh-pressure fuel line, a leakage duct mouth for the connection of theleakage line, and a return flow duct mouth for the connection of thefuel return flow line. This results in the advantage that thehigh-pressure fuel line, the leakage line and the fuel return flow lineare all connected to a joint connection directly on the fuel injector,so that no ducts for removing return flow or leakage amounts from thefuel injector have to be provided in the cylinder head of the internalcombustion engine.

A particularly preferred embodiment of the invention provides that thejoint high-pressure connection has on its face a centrally arrangedhigh-pressure duct mouth for the connection of the high-pressure fuelline and has on its circumference, spaced away from one another in theaxial direction, the leakage duct mouth for the connection of theleakage line and the return flow duct mouth for the connection of thereturn flow line. The individual mouths each are sealed off by sealingelements and separated from the other mouths.

According to a further development, the sealing element of thehigh-pressure duct mouth is formed from a conical seal interacting witha sealing cone constructed at the end of the high-pressure fuel line.The sealing elements sealing off the leakage duct mouth and the returnflow duct mouth are formed from O-rings which interact with the innercircumferential surface of a screw-over sleeve having flowcross-sections which are assigned to the leakage line and the fuelreturn flow line and are spaced away from one another in the axialdirection.

In the following, an embodiment of the invention will be explained bymeans of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a fuel injection system for aninternal combustion engine according to an embodiment of the invention;

FIG. 2 is a slightly schematic longitudinal sectional view of a fuelinjector as used in the described embodiment of the invention;

FIG. 3 is a cross-sectional view of the connection of a common fuelline, which combines the high-pressure fuel line, the fuel return flowline and the leakage line, to a fuel injector in the describedembodiment; and

FIG. 4 is a schematic block diagram of a fuel injection system for aninternal combustion engine with a high-pressure reservoir according tothe prior art.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 4 first describes a fuel injection system for an internalcombustion engine having a high-pressure reservoir to which fuel isadmitted by a high-pressure pump (common rail system). Such a fuelinjection system, which is used particularly for a large-volume dieselengine, contains a high-pressure pump 1 which delivers fuel from a fuelreservoir 2 to a high-pressure reservoir 3. The high-pressure reservoir3 is contained in a high-pressure fuel line 4 connecting thehigh-pressure pump 1 with fuel injectors 5 and operates in the manner ofan oil-elastic high-pressure reservoir. The fuel injectors 5 areprovided for injecting fuel into the combustion space of the internalcombustion engine during an injection operation defined preciselyaccording to the injection start, the injection end and the course ofthe injection. The fuel injectors 5 are controlled by a control unit notillustrated in the figure as a function of the operating condition ofthe internal combustion engine, particularly the rotational speed, theload, the temperature and other parameters. Each fuel injector 5contains an injection nozzle 7 to which the fuel, which is to beinjected, is admitted by way of a fuel duct 6 provided in the fuelinjectors 5. The control of the fuel injector 5 takes place by way of acontrol valve 9 which is constructed as a 3/2-way valve known per se inthe prior art or as a 2/2-way servo valve. For returning fuel, which wasdelivered by way of the high-pressure fuel line 4 but was not injectedby the fuel injectors 5, in the form, for example, of controlquantities, a fuel return flow line 11 is provided which is in each caseconnected to a corresponding connection of each of the fuel injectors 5.Furthermore, a leakage line 12 is connected with each fuel injector 5,which leakage line 12 is used for returning leakage quantities, as, forexample, in the event of a line break and dysfunctional high-pressuresealing points. In the case of a conventional fuel injection system, asillustrated in FIG. 4, the fuel return flow line 11 and the leakage line12 are each provided as independent lines.

FIG. 1 is a schematic block diagram of a fuel injection system having ahigh-pressure reservoir acted upon by a high-pressure pump (common-railsystem) according to an embodiment of the present invention. As in theconventional fuel injection system described in FIG. 4, a high-pressurepump 1 is provided which delivers fuel from a fuel reservoir 2 to ahigh-pressure reservoir 3 which operates in the manner of an oil-elastichigh-pressure reservoir and is contained in a high-pressure fuel line 4which connects the high-pressure pump 1 with fuel injectors 5 forinjecting the fuel into the combustion space of the internal combustionengine. The fuel injectors 5, in turn, contain one injection nozzle 7respectively which is acted upon by way of a fuel duct 6 by the fuel tobe injected held in the high-pressure reservoir 3. The control of theinjection is carried out by a control valve 9 provided in the fuelinjector 5.

According to the invention, a fuel return flow line 11 for returningfuel quantities not injected by the fuel injectors 5 and a leakage line12 for returning leakage quantities occurring at the fuel injectors 5,together with the high-pressure fuel line 4 containing the high-pressurereservoir 3, are combined in a common fuel line 13, as illustrated bythe broken circumference lines in FIG. 1. In general terms, thehigh-pressure fuel line 4, the fuel return flow line 11 and the leakageline 12 are formed by separate flow cross-sections provided in the jointfuel line 13. The construction of the joint fuel line 13 will bedescribed in detail in the following.

FIG. 2 is a slightly schematic longitudinal sectional view of a fuelinjector as it is used in the described embodiment of the fuel injectionsystem according to the invention. The fuel injector, which as a wholehas the reference number 5, comprises an injector housing 10 in which anozzle needle 18 is longitudinally displaceably disposed in a guidingsleeve 25 constructed in the injector housing 10. The tip of the nozzleneedle 18 interacts with an injection nozzle 7 constructed at the lowerend of the injector housing 10 to open and close an injection openingcross-section. In the injector housing 10, a high-pressure duct 19 isconstructed which leads from a high-pressure connection 26 arrangedlaterally on the fuel injector 5 to a nozzle antechamber 22 surroundingthe nozzle needle 18. By way of the high-pressure duct 19, the fuel tobe injected is fed by the high-pressure fuel line 4 illustrated in FIG.1 at a high pressure to the nozzle space 22. The control of the fuelinjector 5 takes place by means of a solenoid 15 arranged at itsrearward end, which solenoid 15 interacts with a control valve formed bya closing body 16 and a valve body 17. By means of the control valve 16,17, a control space 24 is optionally acted upon by fuel supplied at ahigh pressure or is relieved from pressure. The control space 24 isconstructed at the rear side of a needle stilt 23 acting upon the nozzleneedle 18. For removing the control quantities occurring at the controlvalve 16, 17, a return flow duct 21 is provided. A leakage duct 20 isused for removing leakage quantities occurring in the fuel injector 5.To this extent, the construction of the fuel injector 5 illustrated inFIG. 2 corresponds to a fuel injector as currently used by theapplicant.

According to the illustrated embodiment of the invention, it is providedthat the high-pressure connection 26, which is used for the connectionof the high-pressure fuel line 4 illustrated in FIG. 1, is constructedas a common connection which, in addition to a high-pressure duct mouth19 a for the connection of the high-pressure fuel line 4, has a leakageduct mouth 20 a for the connection of the leakage line 12 illustrated inFIG. 1 and a return flow duct mouth 21 a for the connection of the fuelreturn flow line 11 illustrated in FIG. 1. The high-pressure duct mouth19 a for the connection of the high-pressure fuel line 4 is centrallyarranged on the face of the common high-pressure connection 26. Theleakage duct mouth 20 a for the connection of the leakage line 12 andthe return flow duct mouth 21 a for the connection of the return flowline 11 are provided on the circumference of the joint high-pressureconnection 26. The leakage duct mouth 20 a and return flow duct mouth 21a collectively provide the return flow connect 27 and are spaced awayfrom one another in the axial direction. The above-mentioned mouths 19a, 20 a, 21 a of the high-pressure duct, the leakage duct and the returnflow duct are each sealed off and separated from one another by assignedsealing elements.

The construction of the common fuel line 13 and the manner of itsconnection to the joint high-pressure connection 26 of the fuel injector5 will now be explained in detail by means of FIGS. 3a) and b) onconnection with FIG. 2. As illustrated in FIG. 3b), the common fuel line13 (compare FIG. 1) is formed by three line pipes 30, 31, 32 which arecoaxially arranged and surround one another. Of these, the inner linepipe 30 forms the high-pressure fuel line 4. The inner line pipe 30 issurrounded by an inner and an outer jacket pipe 31, 32, which eachenclose a flow cross-section 31 a, 32 a and form the fuel line 11 andthe leakage line 12 (compare FIG. 1). The inner jacket pipe 31surrounding the high-pressure fuel line 30 forms the leakage line 12;the outer jacket pipe 32 surrounding the inner jacket pipe 31 forms thefuel return flow line 11. On their inner surface, the jacket pipes 31,32 are provided with ducts 31 a, 32 a which extend in the longitudinaldirection and which each form the flow cross-sections for the fuelreturn line 11 and the leakage line 12. Between these ducts 31 a, 32 aforming the flow cross-sections, webs 31 b, 32 b are constructed whichrest against the outer circumference of the respective interior pipesurrounded by the corresponding jacket pipe 31, 32. Thus, the webs 31 bof the inner jacket pipe 31 rest against the outer circumference of thehigh-pressure pipe 30, and the webs 32 b of the outer jacket pipe 32rest against the outer circumference of the inner jacket pipe 31.

As illustrated in FIG. 3a), a connecting element, as a whole, markedwith the reference number 28, is provided on the injector-side end ofthe common fuel line formed by the three pipes 30, 31, 32, whichconnecting element establishes a connection between the flowcross-sections 30 a of the high-pressure pipe 30, 31 a of the innerjacket pipe 31 forming the leakage line 12, and 32 a of the outer jacketpipe 32 forming the fuel return line with the assigned mouths 19 a, 20 aand 21 a respectively of the high-pressure duct, the leakage duct andthe return flow duct constructed on the common high-pressure connection26. As illustrated, a sealing cone 37 is constructed at the end of thecentral high-pressure pipe 30. The sealing cone 37 interacts with asealing element in the form of a sealing cone 37 constructed on the faceof the common high-pressure connection 26, as customary per se in thefield of fuel injectors. The mouths 21 a of the return flow duct 21 and20 a of the leakage duct 20 constructed on the circumference of thecommon high-pressure connection 26 are each sealed off and separatedfrom one another by respective sealing elements 34, 35, 36 in the formof O-rings. A screw-over sleeve 38, which is a significant part of theconnecting element 28, contains inner and outer connection ducts 39 and40. The inner connection duct 39 establishes a connection with the flowcross-section 31 a of the inner jacket pipe 31, and the outer connectionduct 40 establishes a connection with the flow cross-section 32 a of theouter jacket pipe 32. The connection ducts 39 and 40 each open out inthe proximity of the mouths 20 a and 21 a of the leakage duct and thereturn flow duct. The sealing elements 33, 34, 35 interact with theinner circumferential surface of the screw-over sleeve 38 such that aflow path is created from the connection duct 40 to the return flow ductmouth 21 a, and a flow path is created from the connection duct 39 tothe leakage duct mouth 20 a.

What is claimed is:
 1. A fuel injection system for aninternal-combustion engine, comprising: a high-pressure pump fordelivering fuel from a fuel reservoir; fuel injectors for injecting thefuel into a combustion space of the internal combustion engine; a commonfuel line including: a high-pressure fuel line having a flowcross-section and connecting the high-pressure pump with the fuelinjectors, the high-pressure fuel line including: a high-pressurereservoir for holding the fuel to be injected, a fuel return flow linefor returning fuel not injected by the fuel injectors, the fuel returnflow line having a flow cross-section, and a leakage line for returningfuel leakage at the fuel injectors, the leakage line having a flowcross-section and surrounding the high-pressure fuel line, wherein theflow cross-sections are separated from one another by walls; and aconnection element for connecting the common fuel line with the fuelinjectors, the connection element having a screw-over sleeve, an innerconnection duct and an outer connection duct.
 2. The fuel injectionsystem according to claim 1, wherein the fuel return line and leakageline surround the high-pressure fuel line, each of the fuel return andleakage lines including ducts on its interior surface, the ductsextending in the longitudinal direction and forming the flowcross-section of the line.
 3. The fuel injection system according toclaim 2, wherein each of the fuel return and leakage lines includes webson its inner surface between the ducts, and the webs resting against theouter circumference of the inner line surrounded by the line.
 4. fuelinjection system according to claim 3, wherein the leakage linesurrounds the high-pressure fuel line and the fuel return line surroundsthe leakage line.
 5. The fuel injection system according to claim 4further comprising a common high-pressure connection that connects thefuel injectors to the high-pressure fuel line, the leakage line and thefuel return flow line, the common high-pressure connection including ahigh-pressure duct mouth for the connection of the high-pressure fuelline, a leakage duct mouth for the connection of the leakage line and areturn flow duct mouth for the connection of the fuel return flow line.6. The fuel injection system according to claim 3 further comprising acommon high-pressure connection that connects the fuel injectors to thehigh-pressure fuel line, the leakage line and the fuel return flow line,the common high-pressure connection including a high-pressure duct mouthfor the connection of the high-pressure fuel line, a leakage duct mouthfor the connection of the leakage line and a return flow duct mouth forthe connection of the fuel return flow line.
 7. The fuel injectionsystem according claim 6, wherein the common high-pressure connectionhas on its face a centrally arranged high-pressure duct mouth for theconnection of the high-pressure fuel line and has on its circumferencethe leakage duct mouth for the connection of the leakage line and thereturn flow duct mouth for the connection of the return flow line, theleakage duct mouth and return flow duct mouth being spaced apart in theaxial direction, wherein each mouth is sealed off by a sealing elementand is separated from the other mouths.
 8. The fuel injection systemaccording to claim 2, wherein the leakage line surrounds thehigh-pressure fuel line and the fuel return line surrounds the leakageline.
 9. The fuel injection system according to claim 8 furthercomprising a common high-pressure connection that connects the fuelinjectors to the high-pressure fuel line, the leakage line and the fuelreturn flow line, the common high-pressure connection including ahigh-pressure duct mouth for the connection of the high-pressure fuelline, a leakage duct mouth for the connection of the leakage line and areturn flow duct mouth for the connection of the fuel return flow line.10. The fuel injection system according to claim 2 further comprising acommon high-pressure connection that connects the fuel injectors to thehigh-pressure fuel line, the leakage line and the fuel return flow line,the common high-pressure connection including a high-pressure duct mouthfor the connection of the high-pressure fuel line, a leakage duct mouthfor the connection of the leakage line and a return flow duct mouth forthe connection of the fuel return flow line.
 11. The-fuel injectionsystem according claim 10, wherein the common high-pressure connectionhas on its face a centrally arranged high-pressure duct mouth for theconnection of the high-pressure fuel line and has on its circumferencethe leakage duct mouth for the connection of the leakage line and thereturn flow duct mouth for the connection of the return flow line, theleakage duct mouth and return flow duct mouth being spaced apart in theaxial direction, wherein each mouth is sealed off by a sealing elementand is separated from the other mouths.
 12. The fuel injection systemaccording to claim 1, wherein the leakage line surrounds thehigh-pressure fuel line and the fuel return line surrounds the leakageline.
 13. The fuel injection system according to claim 12 furthercomprising a common high-pressure connection that connects the fuelinjectors to the high-pressure fuel line, the leakage line and the fuelreturn flow line, the common high-pressure connection including ahigh-pressure duct mouth for the connection of the high-pressure fuelline, a leakage duct mouth for the connection of the leakage line and areturn flow duct mouth for the connection of the fuel return flow line.14. The fuel injection system according claim 13, wherein the commonhigh-pressure connection has on its face a centrally arrangedhigh-pressure duct mouth for the connection of the high-pressure fuelline and has on its circumference the leakage duct mouth for theconnection of the leakage line and the return flow duct mouth for theconnection of the return flow line, the leakage duct mouth and returnflow duct mouth being spaced apart in the axial direction, wherein eachmouth is sealed off by a sealing element and is separated from the othermouths.
 15. The fuel injection system according to claim 1 furthercomprising a common high-pressure connection that connects the fuelinjectors to the high-pressure fuel line, the leakage line and the fuelreturn flow line, the common high-pressure connection including ahigh-pressure duct mouth for the connection of the high-pressure fuelline, a leakage duct mouth for the connection of the leakage line and areturn flow duct mouth for the connection of the fuel return flow line.16. The fuel injection system according claim 15, wherein the commonhigh-pressure connection has on its face a centrally arrangedhigh-pressure duct mouth for the connection of the high-pressure fuelline and has on its circumference the leakage duct mouth for theconnection of the leakage line and the return flow duct mouth for theconnection of the return flow line, the leakage duct mouth and returnflow duct mouth being spaced apart in the axial direction, wherein eachmouth is sealed off by a sealing element and is separated from the othermouths.
 17. The fuel injection system according to claim 16, wherein thesealing element of the high-pressure duct mouth includes a conical sealinteracting with a sealing cone at the end of the high-pressure fuelline, and the sealing elements sealing off the leakage duct mouth andthe return flow mouth each includes an O-ring which interacts with aninner circumference surface of the screw-over sleeve, the screw-oversleeve having flow cross-sections assigned to the leakage line and thefuel return flow line and spaced from one another in the axialdirection.
 18. The fuel injection system according to claim 1, whereinthe inner connection duct establishes a connection with the flowcross-section of the leakage line and the leakage duct mouth of the fuelinjector.
 19. The fuel injection system according to claim 1, whereinthe outer connection duct establishes a connection with the flowcross-section of the return flow line and the return flow duct mouth ofthe fuel injector.